Use of image forming apparatuses such as an MFP (Multi Function Peripheral) enables various kinds of information to be conveniently output in hardcopy, including document copies, facsimile outputs, and printing of PC information. On the other hand, there is a concern over information security for the prevention of forgery and leakage of confidential information.
To this end, there are proposed various information tracking techniques using background printing and monochromatic yellow printing. In one technique, for example, documents are created by background printing, and output information (e.g., output machine number, date and time, and user name) is visualized when the documents are copied. Other techniques include embedding output information in a combination of printed dots, and writing information in documents in a difficult-to-perceive color such as monochromatic yellow.
The attribute information concerning, for example, apparatus and print job, written as secret information in a document is called tracking information.
However, information tracking using techniques such as background printing and monochromatic yellow printing is problematic, because the information is written into a document in visible form, and thus lowers the output image quality. Such deterioration of output image quality can be prevented by lowering the visibility and hiding the information. However, this is also problematic, because the information detection requires a special device.
In MFPs, it is common practice to use the back side of paper, perform double-side printing, and use recycled paper, in order to save paper in consideration of the increasing environmental awareness for protecting the forest resources supplying paper, and reducing the CO2 emission. Further, in MFPs, methods are known that enable paper to be used repeatedly. This is achieved, for example, by mechanically or chemically detaching the image forming material (for example, toner) from paper, or by printing with a decolorizable toner that is decolored by heat, light, or chemicals.
Embodiments described herein are thus concerned with a technique for writing tracking information using an image forming material, such as a toner and an ink, that contains a color material that can be decolored under heat, and that can redevelop color upon cooling.